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The removal of the phenolic compound, caffeic acid, by photodegradation has been investigated using carbon-doped titanium dioxide particles as a photocatalyst under visible light. UV-vis absorption spectroscopy and gas chromatography-ion trap mass spectrometry analyses revealed a substrate concentration dependence of the removal of caffeic acid from a water solution. The k2 and t(0.5) parameters of each reaction were calculated by fitting kinetics data to a second-order kinetic adsorption model. To evaluate the photodegradation event, the effect of the adsorption process on the whole degradation was also monitored in the absence of light. Adsorption isotherm studies supported by ζ potential and scanning electron microscopy data demonstrated the pivotal role of the absorption mechanism. It was found that the whole photodegradation process is governed by a synergic mechanism in which adsorption and photodegradation are involved. This study, centered on the removal of caffeic acid from aqueous solutions, highlights the potential application of this technology for the elimination of phenolic compounds from olive mill wastewater, a fundamental goal in both the agronomical and environmental fields.

Microemulsions have been widely used as microreactors for the synthesis of nanoparticles and mesoporous materials. The correlation between the microstructure of a microemulsion and the features of the obtained materials is the most intriguing problem. On this point, many investigations have their ground on the structure of the precursor microemulsion, i.e., the system before the reaction takes place. Nevertheless, any reactions usually involve the formation of byproducts (aside from the nanoparticles). Several of these byproducts (e.g., ions, amphiphilic molecules) could modify the microemulsion structure during the course of the reaction. Here we examine the hydrolysis of tetraethoxysilane (TEOS) in the water-in-oil microemulsion hexadecyl-trimethylammonium bromide (CTAB)/pentanol/hexane/water. Conductivity and NMR measurements performed during the course of the reaction, in combination with dynamic light scattering and pulsed field gradient spin-echo NMR investigation performed on the microemulsion upon the addition of ethanol, indicate that a byproduct (ethanol) modifies the microreactor structure. The ethanol produced by the TEOS hydrolysis drives the microemulsion structure from small disconnected reverse micelles toward large connected aggregates until (for high enough ethanol loading) the system phase separates into two coexisting liquid phases (a dense interconnected network and a dilute reverse micellar phase).

In this contribution we demonstrate that gelatin can jellify also water-in-oil microemulsions based on the cationic surfactant cetyltrimethylammonium bromide (CTAB). The partial stability diagram of the system CTAB + 1-pentanol + water + hexane + gelatin was determined. The resulting microemulsion-based gels (MBGs) were characterized by means of conductivity and pulsed gradient spin-echo NMR. For the first time the water self-diffusion coefficient was measured in gelatin MBGs, and the results were successfully analyzed in terms of diffusion in an interconnected network of aqueous channels.

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